1. Field of the Invention
This invention relates to methods and apparatus for soldering articles. In particular, articles are immersed in hot vapor to cause the solder to melt and flow to provide a coating and/or bond articles.
2. Description of the Prior Art
It is well known in the prior art to solder coat or bond articles by applying solder to an article in the form of a paste, a preform or the like and immersing the articles into vapor having a temperature at or above the melting point of the solder. Such a process is fully described in U.S. Pat. No. 3,866,307 to Pfahl et al. which issued on Feb. 18, 1975 and is assigned to the instant assignee and Bell Telephone Laboratories, Inc. That patent describes an open-ended vessel having cooling coils about the top portion thereof, a heat transfer liquid within the vessel and heating coils immersed in the liquid. When the heating coils are energized, the heat transfer liquid boils and a body of vapor is formed between the liquid and the cooling coils. Articles to be soldered are immersed in the vapor which condenses thereon, giving up its latent heat of vaporization thereto, causing the solder to flow. The articles are then removed from the vapor to permit the solder to solidify and form a bond between articles.
Such a facility has proven to be eminently satisfactory for soldering a wide variety of articles. However, contaminants such as solder flux or other debris on the articles to be soldered are washed away by the vapor condensate and fall into the heat transfer liquid. Such contaminants come in contact with and befoul the immersed heating coils, resulting in a non-uniform, inefficient heating which can have a deleterious effect on the efficient operation of the facility.